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The vacuum contactor uses the vacuum interrupter to extinguish the arc, which is used to frequently turn on and off the normal working current. It is usually used for 6kV, 380V (660V, 1140V) AC motors that are frequently turned on and off at medium and low voltages.
.3 Working principle
5 Cause of failure
Series low pressure vacuum AC contactors are widely used in coal mines, electric power, metallurgy, and textiles. Various industrial sectors such as high-rise buildings.
Low-voltage vacuum AC contactor for AC: 50HZ. Rated voltage: 1140V, rated current 63 to 630A feed network for long-distance switching and breaking circuits, and frequent starting and stopping of AC motors. It is especially suitable to be assembled into a flameproof electromagnetic starter in combination with various protection devices.
The vacuum contactor is mainly composed of a vacuum interrupter and an operating mechanism. The vacuum interrupter has two functions of reliable arc extinguishing through normal operating current and frequent interruption of operating current. However, the overload current and short-circuit current cannot be cut off. The operating mechanism is composed of a holding coil with an iron core and an armature. The coil is energized to attract the armature and the contactor is closed; the coil is de-energized and the contactor is disconnected. The holding coil is generally in the form of direct current and alternating current.
The outer casing of the vacuum interrupter is made of glass or ceramic insulating material, and the internal vacuum is usually above 0.01 Pa. Since the air inside the casing is small, the contact opening distance can be made small and the arc can be easily extinguished. The contact material is generally made of an alloy of copper, tantalum or niobium. The function of the arc shield in the arc extinguishing chamber is to condense the metal vapor diffused in the gap of the contact when the current is interrupted, which helps to extinguish the arc, and also prevents the metal vapor from splashing onto the insulating shell to reduce the dielectric strength. The movable contact is connected with the lower end of the outer casing by a bellows, and the movable contact can move up and down without leaking.
Vacuum contactors usually consist of an insulating power frame, a metal base, a drive arm, an electromagnetic system, an auxiliary switch, and a vacuum switch tube. When the electromagnetic coil passes the control voltage, the armature drives the arm to rotate, so that the main contact in the vacuum switch tube is turned on, and after the electromagnetic coil is powered off, the main contact is broken due to the action of the opening spring.
The vacuum switch tube is composed of the above cover, the lower cover, the metal bellows and the ceramic tube, and the vacuum switch tube is made of a corrugated porcelain tube made of 95 porcelain insulating material, which has a large creepage distance and high mechanical strength. Heat and impact resistance. A pair of dynamic and static contacts are packaged in the vacuum switch tube, and the contact material is made of Cu-W-Wc with wear resistance and low cutoff value, so that the overvoltage caused by the interception during the breaking process is reduced under the condition of satisfying the breaking performance. The electrical life of the vacuum switch tube is increased. When the metal bellows moves axially, the moving contact is driven to perform the opening and closing action.
The electromagnetic system considers the actual suction characteristics and the reaction force characteristics to be well matched, and exerts the advantages of low noise and power saving during operation of the contactor. The residual double coil is composed of starting and maintaining two windings, and is switched by the auxiliary switch, in order to facilitate the user to communicate. Power operated, the contactor has a bridge rectifier.
Mechanical lock: When the closed coil is energized, the contactor is sucked and the mechanical lock is locked: when the trip coil is energized, the mechanical lock is released, the contactor is released, and the trip coil is in the hot state, the voltage is in Us85 The contactor is reliably released within the range of %-110%.
The vacuum contactor has strong arc-extinguishing ability, good pressure resistance performance, high operating frequency, long service life, no arc external spraying, small volume, light weight and long maintenance period. The vacuum interrupter of the vacuum contactor has a high process requirement, and if the process is poor, the vacuum of the arc extinguishing chamber is liable to decrease. The material of the contact material is not good. When the current is interrupted, the phenomenon of "cut-off over-voltage" will occur. That is, when the current is interrupted, the arc-extinguishing capacity of the vacuum interrupter is very strong, and the arc current is not cut off when the natural zero-crossing occurs, but A certain value of the current suddenly drops to zero, whereby a high overvoltage occurs. The cut-off voltage can jeopardize the safe operation of electrical equipment.
Cause of failure
Whether the vacuum contactor is faulty can be judged according to whether it can be closed, opened and reliably maintained at the closing and opening positions. Faults in the main circuit can be found and eliminated from the routine maintenance and maintenance of the contactor.
The main causes of common failures are analyzed as follows:
Can not store energy: Can not store energy is one of the more common faults of vacuum contactors, especially the energy storage mechanism driven by ratchet and pawl, the probability of failure is high. The energy storage mechanism needs to complete the energy storage operation, which mainly depends on the three parts of the energy storage motor, the drive mechanism and the positioning parts. Grasping these three links, it is easy to find the crux of the failure.
No closing action: There is no closing action failure, which is mainly related to whether the closing electromagnet is sucked, whether the energy storage is in place, and whether the positioning member is in normal operation.
Cavity: There is a closing action but the closing of the gate is called empty. In the analysis of such failures, the analysis should first be carried out from the closing (locking), and then whether it is related to the energy storage part.
Do not open the brakes: It should be emphasized here that when the contactor is refused or cavitation, before analyzing and repairing the main body of the contactor, it is necessary to fully judge whether the cause is in the control and secondary components such as auxiliary switches, terminal blocks, etc. Aspects, then the analytical diagnosis of the contactor.